1. Field of the Invention
The present invention generally relates to an electric power steering system of a vehicle. More particularly, this invention relates to a potentiometer for use in an electric power steering system of a vehicle.
2. Discussion of the Related Art
In an electric power steering system of a vehicle, a potentiometer is linked with a torsion bar spring which receives the steering torque from the steering wheel of the vehicle.
A conventional potentiometer is designed to provide voltage to be supplied to an assist motor in proportion to the steering torque received on the torsion bar spring by sliding a brush device along the surface of an electric resister device in order to change electrical resistance for generation of the output voltage. The assist motor generates torque power corresponding to the voltage supplied from the potentiometer, and assists in steering the front wheels of a vehicle.
The surface of the brush device and the surface of the resister device will eventually get roughened or otherwise deteriorated due to repeated friction between the brush device and the resister device. The roughened and deteriorated surfaces of the brush device and resister device may malfunction by losing adequate physical contact with each other intermittently while in use, resulting in discontinuity or interruption in the performance of the electric power steering system, which will also generate noises in the voltage signals from the potentiometer. Such discontinuity or interruption of the performance of the power steering system may potentially result in serious malfunctioning of the whole system.
Accordingly, it is an object of the present invention to provide a potentiometer for use in an electric power steering system of a vehicle which effectively prevents accidental discontinuity or interruption in the performance of the potentiometer or the electric power steering system.
It is another object of the present invention to provide a potentiometer for use in an electric power steering system of a vehicle which effectively prevents accidental generation of noises in the output voltage signals from the potentiometer.
It is yet another object of the present invention to provide a potentiometer with greatly improved durability and reliability.
Other objects of the present invention will become apparent from the description that follows.
Those and other objects of the present invention will be achieved with a potentiometer of the present invention which is constructed as described hereinbelow.
A potentiometer of the present invention to be used in an electric power steering system of a vehicle does not rely on a brush device or a resister device as a conventional potentiometer does. Instead, the potentiometer of the present invention utilizes a magneto-sensitive device (a magneto-sensitive element or elements) to be placed in a magnetic field generated between a pair of magnetic polar faces of a magnet device. The magneto-sensitive element is generally provided in a rectangular configuration. Other configurations of the magneto-sensitive element will equally function. The potentiometer of the present invention provides an output voltage to an assist motor based on the angular displacement information from the magneto-sensitive element placed in the magnetic field of the magnet device. The magnetic field is affected when the magneto-sensitive element changes its angular position in relation to the direction of the magnetic flux in a manner well known in the relevant art. The assist motor generates power according to the output voltage supplied from the potentiometer, which assists in steering the front wheels of the vehicle as is also known in the related art.
Steering torque generated on the steering wheel of the vehicle is transmitted to a torsion bar spring and twists the torsion bar spring to a degree in proportion to the steering torque. The potentiometer linked to the torsion bar spring utilizes the magnet device described in the above, and outputs voltage in proportion to the twist of the torsion bar spring. The output voltage is utilized by the assist motor.
The potentiometer further comprises a housing having an engagement bore, a magnet casing partially and rotationally engaging the engagement bore of the housing, and an element casing installed co-axially with the engagement bore of the housing. The magnet casing turns an angle in proportion to the twist of the torsion bar spring. The magnet device having a pair of magnetic polar faces is installed centrally in the magnet casing. The magneto-sensitive element is placed in the magnetic field generated between the magnetic polar faces without touching the polar faces.
The potentiometer of the present invention does not rely on frictional elements for its function, which renders the potentiometer of the present invention exceptionally durable and reliable. Discontinuity or interruption and noises in the output voltage from the potentiometer can be effectively eliminated unlike a conventional potentiometer which utilizes a brush device and a resister device.
The magnet device in a preferred embodiment comprises a permanent magnet base and a pair of legs of a magnetic material, each generally having a xe2x80x9cUxe2x80x9d shape. The magnetic legs stretch in parallel respectively from two opposite ends of the magnet base. Each of the free ends of the magnetic legs is provided with a hook portion having a magnetic polar face on its outer end. The magnetic polar faces are provided apart in planar parallel, facing each other.
The magnetic polar faces provide a stable magnetic field therebetween helped by the specific configuration of the generally U-shaped magnet device of the present invention and by the sturdy construction supporting the magnet device. The stable magnetic field or flux effectively helps prevent fluctuation in the output voltage of the potentiometer by eliminating adverse effects to be otherwise caused by oscillation of the magneto-sensitive element due to vehicle vibrations. A certain degree of accidental displacement of the magneto-sensitive element in the xe2x80x9cstablexe2x80x9d magnetic field will be effectively compensated as will be appreciated by ordinary artisans in the related field.
The magnet device may be integrated into the magnetic casing, with the magnetic polar faces exposed, which will reduce fabrication time, and further help stabilize the performance of the potentiometer of the present invention.
The angular position of the element casing which houses the magneto-sensitive element is adjustable in a circumferential direction relative to the housing. This arrangement provides precise setting of the initial output value of the magneto-sensitive element at xe2x80x9cOxe2x80x9d for its neutral position.
The magneto-sensitive element may be electrically connected with an output amplifier and an output adjuster so that any possible fluctuation in the output voltage of the potentiometer may be thoroughly eliminated.
The invention also provides a potentiometer having a means for creating a magnetic field. In additional embodiments, the means for creating a magnetic field comprises a magnet device having two magnetic polar faces which create a magnetic field therebetween.
The invention further provides methods to steer a vehicle using the potentiometer provided herein. One method involves turning a steering wheel that is connected to a torsion bar spring where this turning causes the torsion bar spring to twist by an angle. This twisting causes a potentiometer linked to the torsion bar spring to generate an output voltage in proportion to the twist of the torsion bar. The output voltage is transmitted to an assist motor which steers a wheel on the vehicle. The potentiometer has a magnet device having two magnetic polar faces which create a magnetic field therebetween, and a magneto-sensitive device placed in said magnetic field between the magnetic polar faces. The magnet device is rotatable relative to the magneto-sensitive device in proportion to the twist of the torsion bar spring and changes the relative angle between the magneto-sensitive device and the magnetic field causes the potentiometer to generate voltage for use in generating assist torque.